U.S. patent application number 10/511568 was filed with the patent office on 2005-08-04 for light modulating engine.
Invention is credited to Glent-Madsen, Henrik.
Application Number | 20050168789 10/511568 |
Document ID | / |
Family ID | 29225535 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050168789 |
Kind Code |
A1 |
Glent-Madsen, Henrik |
August 4, 2005 |
Light modulating engine
Abstract
The invention relates to a light illumination apparatus
comprising at least one exposure head (12) and at least two light
modulating arrangements (20), each of said two light modulating
arrangements (20) comprising a spatial light modulator (31, 32) and
an associated light emitter arranged for illumination of an
illumination surface (15) via said spatial light modulator (31,
32), each of said two light modulating arrangements (20) being
digitally controlled, said apparatus comprising means for
performing a relative movement between said at least one exposure
head and said illumination surface (15) in at least one direction
(x;y).
Inventors: |
Glent-Madsen, Henrik;
(Lasby, DK) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Family ID: |
29225535 |
Appl. No.: |
10/511568 |
Filed: |
October 12, 2004 |
PCT Filed: |
April 9, 2003 |
PCT NO: |
PCT/DK03/00237 |
Current U.S.
Class: |
359/237 ;
348/E5.139 |
Current CPC
Class: |
G03F 7/70058 20130101;
G03F 7/70283 20130101; G03F 7/2057 20130101; G03F 7/70291 20130101;
G03F 7/70275 20130101; H04N 5/7416 20130101 |
Class at
Publication: |
359/237 |
International
Class: |
G02F 001/00; G02B
026/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2002 |
DK |
PA 2002 00516 |
Claims
1. Light illumination apparatus comprising: at least one exposure
head; at least two light modulating arrangements, each of said two
light modulating arrangements comprising a spatial light modulator
and an associated light emitter arranged for illumination of an
illumination surface via said spatial light modulator; each of said
two light modulating arrangements being digitally controlled; said
apparatus further comprising means for performing a relative
movement between said at least one exposure head and said
illumination surface in at least one direction.
2. Light illumination apparatus according to claim 1, wherein said
at least two light modulating arrangements are arranged on a single
exposure head.
3. Light illumination apparatus according to claim 1, wherein said
relative movement is a scanning movement.
4. Light illumination apparatus according to claim 1, wherein said
relative movement is established by moving the at least one
exposure head relative to said illumination surface.
5. Light illumination apparatus according to claim 1, wherein said
relative movement is established by moving said illumination
surface relative to the at least one exposure head.
6. Light illumination apparatus according to claim 1, wherein the
at least one exposure head comprises the two light modulating
arrangements.
7. Light illumination apparatus according to claim 1, wherein said
light modulating arrangements are arranged on at least two
different exposure heads and where said exposure heads perform
scanning movements over the illumination surface.
8. Light illumination apparatus according to claim 1, wherein said
spatial light modulators are arranged so as to illuminate at least
two substantially separate sub-areas of said illumination
surface.
9. Light illumination apparatus according to claim 1, wherein said
spatial light modulating arrangements are aligned so that rows of
both light modulators are parallelly oriented.
10. Light illumination apparatus according to claim 1, wherein said
spatial light modulating arrangements are aligned so that
neighboring rows of the at least two spatial light modulators are
positioned substantially so that a distance between the neighboring
rows of the at least two spatial light modulators is substantially
the same as a distance between rows of the individual light
modulators.
11. Light illumination apparatus according to claims 1, wherein an
"x-projection" of a distance between centers of at least two of the
spatial light modulators is less than approximately 200
millimeters.
12. Light illumination apparatus according to claim 1, wherein a
"y-projection" of a distance between centers of two of the spatial
light modulators is less than approximately 50 millimeters.
13. Light illumination apparatus according to claim 1, 4, wherein a
distance between centers of two of the spatial light modulators is
substantially 122.7 millimeters or 121.73 millimeters when applying
SXGA and XGA respectively.
14. Light illumination apparatus according to claim 1, wherein said
exposure head comprises cooling means.
15. Light illumination apparatus according to claim 1, wherein each
spatial light modulating arrangement comprises individual cooling
means.
16. Light illumination apparatus according to claim 1, wherein said
substantially separate sub-areas comprise neighboring surfaces of
said illumination surface.
17. Light illumination apparatus according to claim 1, wherein said
at least one direction is substantially transverse to a relative
movement of said illumination surface.
18. Light illumination apparatus according to claim 1, wherein said
at least one direction establishes that an illuminated pixel on
said illumination surface is illuminated by means of a least two
light modulators of said spatial light modulator.
19. Light illumination apparatus according to claim 1, wherein said
at least one direction establishes that an illuminated pixel on
said illumination surface is illuminated by means of at least one
modulator row of said spatial light modulator.
20. Light illumination apparatus according to claim 1, wherein said
exposure head is movable in at least two directions with respect to
said illumination surface.
21. Light illumination apparatus according to claim 1, wherein said
light emitter comprises a light source.
22. Light illumination apparatus according claim 1, wherein said
light emitter comprises at least one light emitting end of an
optical guide coupled to a light source.
23. Light illumination apparatus according to claim 1, wherein said
light emitter comprises a lamp.
24. Light illumination apparatus according to claim 1, wherein said
light emitter comprises an a LED matrix.
25. Light illumination apparatus according to claim 1, wherein said
spatial light modulator comprises a DMD chip.
26. Light illumination apparatus according to claim 1, wherein said
spatial light modulator comprises a micro-mechanical transmissive
light modulator.
27. Light illumination apparatus according to claim 1, wherein said
illumination surface comprises a printing plate.
28. Light illumination apparatus according to claim 1, wherein said
illumination surface comprises a light sensitive material.
29. Light illumination apparatus according to claim 1, wherein the
exposure head is adapted for scanning in two transverse opposite
directions.
30. Light illumination apparatus according to claim 1, wherein an
x-direction between centers of the spatial light modulating
arrangement is less than 150 mm.
31. Light illumination apparatus according to claim 30, wherein the
x-direction between centers of the spatial light modulating
arrangement is substantially.
32. Method of illuminating an illumination surface, whereby at
least two light modulating arrangements arranged on at least one
exposure head, each comprising a spatial light modulator illuminate
an illumination surface by a scanning movement.
33. Method of illuminating an illumination surface according to
claim 32, whereby said at least two light modulating arrangements
are arranged on a single exposure head.
34. Method of illuminating an illumination surface according to
claim 32, whereby said at least two light modulating arrangements
are arranged on different free-running exposure heads.
35. Method of illuminating an illumination surface, whereby the
illumination is performed by a light illumination apparatus
according to claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a light illumination
apparatus according to claim 1.
BACKGROUND OF THE INVENTION
[0002] A typical light illumination apparatus comprises an
arrangement adapted for illuminating a light sensitive material.
Such material may e.g. comprise printing plates, materials adapted
for rapid prototyping, film, etc. The illuminating is performed for
the purpose of obtaining certain changes of properties of the
illuminated material. Such illumination may thus e.g. result in the
establishment of an image on the illuminated material or a certain
structure.
[0003] In order to obtain the desired illumination, light must be
modulated. One prior art method of modulating light transmitting to
an illumination surface is to apply a single or multiple beam
laser, which may be modulated when performing a scanning movement
over the illumination surface.
[0004] Another and more recent way of illuminating an illumination
surface is to apply a so-called spatial light modulator. Examples
of such modulators may be a DMD, an LCD, etc. The spatial light
modulator is adapted for modulating an incoming light beam into a
number of individually modulated light beams.
[0005] A problem of the prior art is that the obtainable modulating
speed is somewhat limited due to the nature of the applied light
modulators combined with the required energy and illumination speed
for some applications.
SUMMARY OF THE INVENTION
[0006] The invention relates to a light illumination apparatus
comprising at least one exposure head and at least two light
modulating arrangements, each of said two light modulating
arrangements comprising a spatial light modulator and an associated
light emitter arranged for illumination of an illumination surface
via said spatial light modulator,
[0007] each of said two light modulating arrangements being
digitally controlled,
[0008] said apparatus comprising means for performing a relative
movement between said at least one exposure head and said
illumination surface in at least one direction.
[0009] According to the invention it has been realized that a
movable exposure head may advantageously comprise two spatial light
modulators, thereby facilitating a scanning by means of a two
modulators at one time.
[0010] In an embodiment of the invention, the light illumination
apparatus comprises at least one exposure head and at least two
light modulating arrangements
[0011] each of said two light modulating arrangements comprising a
spatial light modulator and an associated light emitter arranged
for illumination of an illumination surface via said spatial light
modulator,
[0012] each of said two light modulating arrangements being
digitally controlled,
[0013] said apparatus comprising means for performing a relative
movement between said at least one exposure head and said
illumination surface in at least one direction.
[0014] In an embodiment of the invention, said at least two light
modulating arrangements are arranged on the same exposure head.
[0015] In an embodiment of the invention, said relative movement is
a scanning movement.
[0016] In an embodiment of the invention, said relative movement is
established by moving the at least one exposure head relative to
said illumination surface.
[0017] In an embodiment of the invention, said relative movement is
established by moving said illumination surface relative to the at
least one exposure head.
[0018] In an embodiment of the invention, at least one exposure
head comprises two light modulating arrangements. It has thus been
established that a cost-effective way of illuminating an
illumination surface is by applying two spatial light modulation
arrangements in one exposure head, thereby obtaining an
illumination arrangement, which may illuminate the illumination
surface in a relatively high-speed scanning movement. In this
context is noted that an exposure head may be somewhat difficult to
deal with when the weight of the moving arrangement increases.
[0019] In an embodiment of the invention, said relative movement is
established by moving said illumination surface relative to the at
least one exposure head.
[0020] In an embodiment of the invention, at least one exposure
head comprises two light modulating arrangements.
[0021] In an embodiment of the invention, said light modulating
arrangements are arranged on at least two different exposure heads
and where said exposure heads perform scanning movements over the
illumination surface. When applying two or more free-running
scanning exposure heads, the illumination may be optimized
carefully to the illumination surface, thereby avoiding so-called
"over-scanning". In principle, any superfluous scanning may be
avoided or at least minimized due to the fact that the scanning
performed by the exposure heads may be adapted to avoid any
conflicting movement between the applied exposure heads. Thus, a
number of free-running exposure heads illuminating an illumination
surface by scanning is quite advantageous with respect to
efficiency due to the fact that the scanning movement as such
ensures a high-speed illumination, while the free-running heads
ensure that the illumination of the illumination area may be
optimized as described above.
[0022] According to a further embodiment of the above-described
free-running exposure heads, the number may exceed two, e.g. three
or further heads in total. Moreover, each head may e.g. comprise
two or further illumination arrangements, e.g. of the type
described in FIG. 2.
[0023] When said spatial light modulators being arranged so as to
illuminate two substantially separate sub-areas of said
illumination surface, an advantageous embodiment of the invention
has been obtained.
[0024] When said spatial light modulating arrangements being
aligned so that the rows of both light modulators are parallelly
oriented, an advantageous embodiment of the invention has been
obtained.
[0025] When said spatial light modulating arrangements being
aligned so that the neighboring rows of the two spatial light
modulators are positioned substantially so that the distance (DN)
between the two neighboring rows of the two spatial light
modulators are substantially the same as the distance (DR) between
the rows of the individual light modulators, an advantageous
embodiment of the invention has been obtained.
[0026] When the "x-projection" (D1) of the distance between the
centers of the two spatial light modulators being less than 200
millimeters, preferably less than 150 millimeters, preferably
substantially 120 millimeters, an advantageous embodiment of the
invention has been obtained.
[0027] When the "y-projection" (D2) of the distance between the
centers of the two spatial light modulators being less than 50
millimeters, preferably less than 35 millimeters, preferably
substantially 25.6 millimeters or 20.5 millimeters when applying
SXGA, and XGA respectively, an advantageous embodiment of the
invention has been obtained.
[0028] When the distance between the centers of the two spatial
light modulators being less than 121.73 millimeters (XGA) or 122,70
millimeters (SXGA), an advantageous embodiment of the invention has
been obtained.
[0029] According to the invention it has been recognized that a
very close positioning of the light modulating arrangements
facilitates an improved overall scanning speed in the sense that
the effective scanning area is optimized. A minimizing of the
distance therefore results in that both spatial light modulators of
the exposure head are active as long as possible at the ends of the
scanning lines.
[0030] When said exposure head comprising cooling means, an
advantageous embodiment of the invention has been obtained.
[0031] Cooling means may e.g. comprise electrically driven
fans.
[0032] When each spatial light modulating arrangement comprising
individual cooling means, an advantageous embodiment of the
invention has been obtained.
[0033] When said substantially separate sub-areas comprising
neighboring surfaces of said illumination surface, an advantageous
embodiment of the invention has been obtained.
[0034] When said at least one direction being substantially
transverse to a relative movement of said illumination surface, an
advantageous embodiment of the invention has been obtained.
[0035] When said at least one direction establishing that an
illuminated pixel on said illumination surface is illuminated by
means of a least two light modulators of said spatial light
modulator, an advantageous embodiment of the invention has been
obtained.
[0036] When said at least one direction establishing that an
illuminated pixel on said illumination surface is illuminated by
means of at least one modulator row of said spatial light
modulator, an advantageous embodiment of the invention has been
obtained.
[0037] When said exposure head being movable in at least two
directions with respect to said illumination surface, an
advantageous embodiment of the invention has been obtained.
[0038] When said light emitter comprising a light source, an
advantageous embodiment of the invention has been obtained.
[0039] When said light emitter comprising at least on light
emitting end of an optical guide coupled to a light source, an
advantageous embodiment of the invention has been obtained.
[0040] When said light emitter comprising a lamp, an advantageous
embodiment of the invention has been obtained.
[0041] When said light emitter comprising a LED matrix, an
advantageous embodiment of the invention has been obtained.
[0042] When said spatial light modulator comprising a DMD chip, an
advantageous embodiment of the invention has been obtained.
[0043] The spatial light modulating array of the illumination
arrangements may be a transmissive micro-mechanical shutter array
as disclosed in WO 98 47048 and WO 98 47042, which are hereby
included by reference.
[0044] Another type of spatial modulator may be a DMD modulator or
e.g. LCD light modulator.
[0045] When said spatial light modulator comprising a
micro-mechanical transmissive light modulator, an advantageous
embodiment of the invention has been obtained.
[0046] When said illumination surface comprising a printing plate,
an advantageous embodiment of the invention has been obtained.
[0047] When said illumination surface comprising a light sensitive
material, such as epoxy, an advantageous embodiment of the
invention has been obtained. Other light sensitive materials may be
applied as well within the scope of the invention such as emulsions
for silkscreen printing, PCB emulsions, etc.
[0048] According to the invention, the illumination arrangement may
be applied for so-called rapid prototyping.
[0049] Moreover, the invention relates to a method of illuminating
an illumination surface whereby at least two light modulating
arrangements arranged on at least one exposure head, each
comprising a spatial light modulator illuminate the illumination
surface by a scanning movement.
[0050] In an embodiment of the invention, said at least two light
modulating arrangements are arranged on the same exposure head.
[0051] In an embodiment of the invention, said at least two light
modulating arrangements are arranged on different free-running
exposure heads.
[0052] In an embodiment of the invention, the illumination is
performed by means of a light illumination apparatus according to
any of the claims 1-31.
THE FIGURES
[0053] The invention will be described in the following with
reference to the drawings where
[0054] FIG. 1 illustrates a view of an exposure system, according
to an advantageous embodiment of the invention,
[0055] FIG. 2 illustrates a cross-section of an illuminating
arrangement, according an embodiment of the invention,
[0056] FIG. 3a illustrates a scanning pattern of an exposure head
with respect to an illumination surface and where
[0057] FIG. 3b illustrates a further scanning pattern of an
exposure head with respect to an illumination surface
[0058] FIG. 4a illustrates an advantageous positioning of the
illuminating arrangements on the exposure head and where
[0059] FIG. 4b-4c illustrate further embodiments of the
invention.
DETAILED DESCRIPTION
[0060] FIG. 1 illustrates a view of a few main components of an
exposure system, according to an advantageous embodiment of the
invention.
[0061] The illustrated system comprises an exposure head 12
comprising two illumination arrangements 20 arranged for
illumination of an illumination surface 15. The exposure head 12 is
suspended in a suspension (not shown). The suspension facilitates
movement in the direction of the arrows under control by suitable
electronic circuits (not shown).
[0062] For illustrative purposes, two illumination areas I1, I2
illuminated by the spatial light modulators (e.g. DMD chips)
arranged in the illumination arrangements 20 are indicated on the
illumination surface. The illumination areas I1 and I2, may e.g.
comprise 1024.times.768 (XGA) pixels or 1280.times.1024 pixels
(SXGA) if applying e.g. TI DMD-chips. The modulated pixels will, if
applying a scanning movement, be switched dynamically from row to
row (or column to column) thereby applying several pixels (e.g. a
complete row of a spatial light modulator) for illumination of a
single pixel on the illumination surface. Thereby, the delivered
optical energy to a single pixel is increased.
[0063] According to the illustrated embodiment, the exposure head
is moved in the X-direction and the illumination surface 15 is
moved stepwise in the Y-direction.
[0064] Evidently, other relative movements may be applied within
the scope of the invention. A further advantageous embodiment of
the invention may e.g. imply a relative movement of the exposure
head 12 in both directions X and Y while keeping the illumination
surface stationary.
[0065] The spatial light modulating array of the illumination
arrangements may be a transmissive micro-mechanical shutter array
as disclosed in WO 98 47048 and WO 98 47042, which are hereby
included by reference.
[0066] Another type of spatial modulator may be a DMD
modulator.
[0067] FIG. 2 illustrates a preferred embodiment of one of the
light modulating arrangements 20 of FIG. 1. The first part 21 of
the arrangement 20 produces a focused and uniform beam of light. It
comprises a lamp 210, a lamp driver 211, a blower 216 and a fan
217, a protection glass 212, a shutter 213, a light-integrating rod
214 and beam shaping optics 215.
[0068] The type of lamp 210 depends on the type of plate to be
exposed. Possible types comprise conventional short arc bulbs,
laser sources, diode arrays and more. A preferred conventional lamp
might have a power consumption of 270 W, but the present invention
is not in any way limited to this value, nor to the mentioned types
of lamps. Alternatives such as 250 W and 350 W may be
considered.
[0069] The light from the lamp 210 is transmitted through a filter
(e.g. IR or UV-filter depending on the application) 212,
functioning as an interference filter, and through a shutter
mechanism 213, making it possible to turn off the light beam
without turning off the lamp. This is important as most lamp types
need time before their light intensity and frequency is unvarying.
A blower 216 and a fan 217 ensure the cooling of the lamp 210.
[0070] Subsequently the light beam is transmitted through a
light-integrating rod 214. Thereby the light is mixed, making the
light throughout the beam uniform with regards to intensity. This
ensures that the light in the periphery of the beam has the same
intensity as the light in the center of the beam. When the light
leaves the light-integrating rod 214, the beam shaping optics 215
focuses it.
[0071] The next part of the arrangement 20 modulates the light beam
to reflect electronically stored image data. It comprises a
light-modulating means 22 and means 224 for directing the
unmodulated light beam towards the light-modulating means 22
without disturbing its modulated light beam output.
[0072] Suited light-modulating means 22 comprises DMD modulators,
transmissive shutters including LCD and micro-mechanical shutters
and more. For the preferred embodiment of FIG. 2, a DMD
light-modulating chip 220 mounted on a PCB 221 with a cooling plate
222 and a temperature sensor 223 is used.
[0073] The light directing means 224 depends on the type of
light-modulating means 22 used. For transmissive light modulating
means the unmodulated light beam is directed towards one side of
the light modulating means, and the modulated light beam is emitted
from the other side. In such an arrangement the light directing
means 224 might be excluded.
[0074] For DMD modulators the unmodulated light beam is directed
towards the same point as where the modulated light beam is
emitted. This necessitates the use of light directing means 224. In
the preferred embodiment of FIG. 2, a TIR-prism is used for light
directing means. TIR is an abbreviation meaning `Total Internal
Reflection`. A TIR-prism comprises a surface 225 which will act as
a mirror to light coming from one direction (from the left for this
specific embodiment), and will let light coming from another
direction (from the top for this specific embodiment) straight
through.
[0075] The last part of the arrangement 20 focuses the multiple
modulated light beams emitted from the light modulating means 220
on an illumination surface 24 (printing plate). It comprises a set
of lenses/a macro lens 230 located within a housing 23. FIG. 3a
illustrates a scanning pattern of an exposure head with respect to
an illumination. The illustrated scanning pattern obtained by the
light illumination apparatus according to the invention, e.g. the
illumination arrangement as described in FIG. 2, involves that two
illuminating arrangements 31, 32 of an exposure head 30a perform a
relative movement with respect to an illumination surface. Both
illumination arrangements 31, 32 are arranged on the same exposure
head 30a.
[0076] One of the illustrated illumination arrangements 31
illuminates the sub areas SUB1 and the other illumination
arrangement 32 illuminates the sub areas SUB2.
[0077] It should be noted that the exposure head 30a illuminates
the illumination surface by modulated light in both directions in a
scanning movement as indicated by the horizontal arrows while
shifting between each scanning movement in steps 301, as indicated
by the vertical arrow.
[0078] The y-axis movement is here performed as steps corresponding
to the total transverse scanning width obtained by both light
illuminating arrangements in combination.
[0079] FIG. 3b illustrates a further scanning pattern of an
exposure head 30b with respect to an illumination surface.
[0080] According to the illustrated embodiment of the invention, an
exposure head 30b comprises two spatial light modulators 31, 32
(the illumination arrangements carrying the spatial modulators are
not illustrated). The applied illumination arrangements 31, 32 may
e.g. both be the illustrated illumination arrangement of FIG. 2.
According to the illustrated embodiment, two spatial light
modulators 31, 32 (or the resulting illuminated surface
corresponding to I1, and I2 of FIG. 1) are arranged and displaced
only in the Y-direction.
[0081] The exposure head 30b is performing a scanning movement back
and forth in the X-direction. Moreover, the illumination surface or
the exposure head performs a relative movement in the Y-direction
involving basically two different steps, a micro step 302 and a
macro step 303.
[0082] According to the illustrated embodiment, eight sub-areas
SUB1 and eight sub-areas SUB2 are illuminated by performing the
micro-steps 302. Thereafter, a macro step 303 is performed and a
new set of sub-areas, SUB1 and SUB2, is illuminated by performing
further micro steps 302.
[0083] It should be emphasized that several other scanning methods
(patterns) may be applied within the scope of the invention.
[0084] FIG. 4a illustrates an advantageous positioning of the
illuminating arrangements (here=optical engines) on the exposure
head of e.g. FIG. 3a. The illumination arrangement 20, which e.g.
may be the one illustrated in FIG. 2, is indicated by dashed
lines.
[0085] The dimensions of the optical engine are very important for
the productivity and cost of the machine. The two illuminating
arrangements 20 of the exposure head are located so that the
obtainable illuminated areas are adjacent in the direction of the
y-axis (not to be confused with the scanning and modulator axis).
This implies that there is a center distance between the optical
engines in the x-axis, see FIG. 4a.
[0086] The mutual distance between the engines in the x-axis
implies that it is necessary to expose longer than the actual plate
length so that both heads have passed the entire plate (the
illumination surface). This superfluous "over-scan" is twice the
center distance D1. This over-scan reduces the productivity and
increases the width of the x-movement and thus the width of the
machine. The center distance must therefore be as low as possible.
An example of such minimized distance may e.g. be
Center distance, x-axis: D1=120 mm
Center distance, y-axis: D2=(XGA) 20.48.+-.0.002 mm and D2
(SXGA)=25.6.+-.0.002 mm
[0087] The lower limit is defined by the optics and the further
illumination arrangement component, e.g. the macro lens 230 of FIG.
2. A fixture (not shown) will allow adjustment in the illumination
plane, i.e. adjustment in x- and y-axis, and rotation about the
z-axis, of the optical engines individually. This implies that the
image must be accurately parallel to the flange of the macro lens
house, so that both images will be in the same plane. The flange on
the house is used to mount the house to the fixture, in the
z-direction. The bottom side of the flange will define the focus,
so that the optical engines can be mounted against a flat surface,
and thus having focus in the same plane.
[0088] FIG. 4b illustrates a further embodiment of the invention,
where the apparatus comprises four light modulating arrangements
53, 54, 55, 56, e.g. of the type illustrated in FIG. 2, arranged on
an exposure head 50.
[0089] The four light modulating arrangements 53, 54, 55 and 56 all
move together due to the fixation to the same exposure head. A
scanning may advantageously be performed in several different ways,
e.g. according to the principles illustrated in FIG. 3a.
[0090] FIG. 4c illustrates a further embodiment of the invention,
where the apparatus comprises two light modulating arrangements 62,
63, e.g. of the type illustrated in fig.2.
[0091] The illustrated embodiment comprises two separate exposure
heads 60, 61, each carrying a modulating arrangement 62, 63.
[0092] The illustrated embodiment of the invention has the
advantage that the illumination, when applying a scanning e.g. in
the direction of the illustrated arrows, may be optimized carefully
to the illumination surface, thereby avoiding the above-described
"over-scanning". In principle, any superfluous scanning may be
avoided due to the fact that the scanning performed by the exposure
heads 60, 61 may be adapted to avoid any conflicting movement
between the applied exposure heads 60, 61.
[0093] The illustrated embodiment, featuring a number of
free-running exposure heads illuminating an illumination surface by
scanning, is quite advantageous with respect to efficiency due to
the fact that the scanning movement as such ensures a high-speed
illumination, while the free-running heads ensure that the
illumination of the illumination area may be optimized as described
above.
[0094] Evidently, the embodiment of FIG. 4c may be modified to
incorporate fisher illumination heads, e.g. three or further heads
in total.
* * * * *